Gastight instrument shell for furnaces



July 22, 1958 A. E. BOREL ETAL GASTIGHT INSTRUMENT SHELL FOR FuRNAcEsFiled Aug. 3l. 1955 \\M\W\W\ II VIII', rf/IVAafg V/ .f9.4 F196 Figa 4agastight shell or cover. thermoplastic bodies, such as glasses andenamels are A p 12,844,637," Y GASTIGHT INSTRUMENT SHELL FOR FURNACESAlfred Eao'uanrBureL-'Neucharet and Jeamrierre Borel,

y Application August s1, 1953, lserial No. 377,646

. AClaimspriority;application Switzerland Septemb'er5,19 52T vOurjpre'ls'ent invention relates to' a'shellldestinedto make gastight 'adefined space in'a fur'race. o ,l

' In order to measure, for example, the temperature in industrialfurnaces, thermo-electric 4elements lcommonly are used which usually areprotected by an exterior tube :made -of'fimjetalw'orceramr'cm'aterial.If, however, the

furnaceratmosphere comprises, for example, sulfurous gases or carbonicoxide, vor if the -therm'o-'electri'c'elem'ent .and its protector .tubeareimmersed, r`for example, in f saline cementation or 'hardening baths,the gases pass through'the protectortubeeither by reason of itsporosityyor byfdeep -cem'entation or, again, by chemical proximitytransmissionand generally attack thelthermo-electric elenient :and.modify 'itsiindications The' same disturbing effects arise when anoptical vtemperature-measuring in- Vstrument is used in place of thethermo-electric element.

The main object of our present invention is to provide We havel foundthat certain gastight.

`The shell forming the subject. matter of our present invention ischaracterized in that it comprises a coat of thermoplastic gastightmaterial.

Four examples of our invention are shown in the accompanying drawing, inwhich- Figs.` 1, 3, 5 and'7 are longitudinal sections of which eachshows schematically one example, and

Figs. 2, 4, 6 and 8 are cross-sections corresponding to i the Figs. l,3, 5 and 7 respectively.

The examples have been limited to the case where the shelly whichforms'the subject matter of our present invention, is destined toprotect a thermo-electric element 1. Such shell, however, obviously alsomay serve to protect an optical temperature-measuring instrument or topermitto thermally treat an object in -a controllable atlnosphereindependent of the operating temperature.

In the first form of the invention (Figs. l and 2), the protector shellof the thermo-electric element 1 comprises an outer tube 2, an innertube 3 of the same material I(4) its adherence to said tubes shall bejpositiv The two following examples give the chemical sition of aparticularly suitable thermoplastic'rnateiialthe t rfirst beingsuitablefor use withjtubes'-joffchrolne-v lated steel, andkthel secondfor useV with yf material. Y y I v Example l ,S-02 A1203 F3203 CaO MgONago Kao. B203?" The yglassl obtained vbyl such `composition, 'Sconstituents may vary upto 15%; :possesses a hi-ghi, cofV eliicient ofthermal expansion, andthe-shellobtainedlin this way'is particularlysuitable for measuring'elevated This composition is that of a glass ofthe type Pyrex and has a low coeicient of thermal expansion. If themeas-V uring instrument mentioned above is to `be used for rela-v tivelylow temperatures, i. e. below 800 C., preferably an enamel is chosen asthermoplastic materialwhich hasy the usual composition.

In the lirst example of shell mentioned above in con` 7 nection withFigs. l and 2, recesses 5 are provided on the interior tube 3 in orderto maintain the latter coaxial with tube 2, since the material of coat 4is softened under normal operating conditions and the inner tube thus isfree to move laterally.

The second example of shell, shown inl Figs. 3 and 4,`

v only differs from the first in that the coat 4a of 'thermo-V as'theouter tube, and a coat 4 of gastight thermoplastic y material whichfills the entire space between the two tubes 2 and 3. The tube 2 comesin contact with the furnace atmosphere or with the bath and normally ismade 'of metal. If, however, this tube is intended for contact with alsulfurous flame or an atmosphere which attacks metal, or if the tube isimmersed in ya bath which is in contact ,with a source of electricenergy of elevated voltage, it is made of ceramic material.

The thermoplastic material 4 is chosen to satisfy the.

following four requirements: f

(l) Its coefcient of thermal expansion shall be substantially the sameas that of the tube material;

(2) it shall soften at the operating temperatures of the shell so as tobe able to better follow the expansions of the two tubes;

(3) its temperature of devitrilication shall be exceeded under normaloperating conditions so as to preserve its vitrous character;

plastic material does not entirely fill the space between the two tubes2 and 3, but merely covers the interior wall of outer tube 2. o l

In order to ensure the transmission of the heat through the spacebetween coat 4a :and inner tube 3, such Vspace may be filled by a bodyin powder form or by'a body l which is liquid at the operatingtemperatures Yof .said instrument, in order that the coefficient ofexpansion of the filler material does not create any complications.,` Ametal well suited for such filler is tin. .Molten tin does not adhere toglass, and although such tin coat is in fusion and the coat ofthermoplastic material is softened, the latter adheres suiciently strongto the Wall of tube 2,

through capillarity and affinity with the ferrous oxidesto avoid theformation of convection streams.: between said material and the moltentin in the space between theV two tubes 2 and 3. Such disposition givesasatisfactory thickness of the coats of thermoplastic material andfiller, such thickness being substantially the same forbothmaterials andof the order of from one to -two millimeters.

The third example (Figs. 5 and 6) onlydilers from the second example inthat the coat 4b of 'thermoplastic material covers the outside of innertube 3.A The space L between coat 4b and tube 2 may be leftvoid kor lledby a body in the form of powderor a metal which` f f 2,844,637. -l""retreated-ojJalyazllgs l' liquid at the operating temperatures of saidinstrument.

In the fourth example (Figs.f7 and 8) the protector shell compises` onlyan outer tube 2, and the thermoelectric lelement 1 is surrounded bythermoplastic material 4c which fills the en tire space outside of saidelement 1 in tube 2.

In the four examples of the subject matter of our present inventiondescribed above, .the gases or cementing products .may transform thestructure of the material of outer tube 2, but the coat of thermoplasticmaterial present in the latter prevents the gases from entering into thespace containing the thermo-electric element. Thus the desiredatmosphere may be maintained in said space. Obviously, the shell mayhave another form than the one shown, although the cylindrical form isthat which lends itself best to the manufacture of the diierent parts ofthe shell.

What We claim as `new and desire to secure by Letters Patent is:

1. A thermocouple adapted for use within a furnace at temperatures inthe range of 800 to 1200 C. comprising a pair of similar nested gaspervious metal tubes having spacedvproximate Walls and being closed atone end, an adherent layer of yglass impermeable to gases interposedbetween said walls and having a coeicient of thermal expansionsubstantially equal to that of each of said tubes, said materialsoftening Within said temperature range and each of said tubes having asoftening temperatur'eabove 1200 C., and a thermoelectric responsiveelement disposed within `said tubes.

' 2. A thermocouple as set forth in claim 1 wherein at least one of saidtubes is composed of chrome plated steel.

3. A thermocouple as set forth in claim 1 wherein said glass hasapproximately the following composition: 68% sio2, 4% A1203, 0.7% 11.3206% Cao, 0.5% Mgo,

N320, KZO, and B203.

4. A thermocouple as set forth in claim 1 wherein said glass hasapproximately the following composition: 80% SiOz, 4% Na2O, 1% KZO, 2%A1203, 0.5% CaO, 0.1% MgO, and 12% B203.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Lange, N. A.: Handbook of Chemistry, Handbook Publishers,Inc., Sandusky, Ohio, Ed. 7, 1949, page 179.

Norton, F. H.: Elements of Ceramics, Addition-Wesley Press, Inc.,Cambridge, Massachusetts, 1952, page 156.

